Everyone talks about bearings, and even can point to things that are ball bearings, or other sorts. Not everyone, however, really understands what a bearing does. A bearing is nothing more than a device to support the weight or thrust of an object, without interfering with its motion.
In most instances that the average American will be familiar with a bearing is nothing more than a sealed ring around a shaft where metal balls packed in grease allow the shaft to rotate while supporting the weight of the shaft. This species is called a ball bearing, and it is very effective for low to moderate weight loads, or low-speed loads.
Other kinds of bearings may use metal rollers instead of metal balls to provide more support than the ball bearings could. And ball and roller bearings may be both open to the environment or closed. But, these are not suitable for all purposes: because there is little provision for cooling, especially, ball and roller bearings are not suitable for high speed, high pressure situations.
In those situations a lubricated bearing is necessary. Examples of lubricated bearings include the bearings of the drive shaft of one’s automobile or the shafts of a turbine generator in a power generation plant. The purpose of these lubricated bearing systems is twofold: first, to support the weight of the shaft while still allowing it to turn freely; second, to cool the bearing and shaft and prevent heat damage to the materials of the bearing or shaft.
Lubricated bearings come in two types: forced circulation and open reservoir lubricated bearings. In the automobile engine, the bearings that support the drive shaft of the engine are open reservoir bearings: As the motor operates the oil in the oil pan is carried through the moving parts of the engine to flow down to where it is needed to lubricate and cool the bearings and surfaces of the engine in a haphazard manner,
with no specific provision made to force the oil through any given bearing. A forced circulation system, on the other hand, pumps the oil through all the bearings of the system, cooling the bearing material and the shafts at the same time. This is the system used on power plant turbines.
In each of these systems the lubrication is vital, not only does it provide necessary cooling, but the lubricant is actually providing a layer of molecules between the shaft and the bearing to keep the two metal surfaces from touching and wearing each other away. When one considers that tolerances within a steam turbine are calculated within thousandths of an inch, it becomes easy to see why any unnecessary wear would be a bad thing.
Not only that, but the lubricated bearings also provide a final seal between the turbine’s high and low-pressure areas and the work environment around the turbine. Losing that seal would, at best, reduce the efficiency of the turbine and at worst, could make the workspace around the turbine uninhabitable, until it had been shut down, and repaired.
There is one final type of bearing I’d like to mention and that is the Kingsbury thrust bearing: This is a bearing specifically designed to allow thrust to be absorbed by a shaft without causing misalignment to the rest of the system. This is the bearing that makes it possible for a propeller-driven ship to move through the water without pushing the turbines out of alignment. And, like most large system bearings, it is another forced lubrication bearing.